The intercistronic region between the rIIA and rIIB genes of the bacteriophage T4 is being studied. This region contains an rIIA translational termination signal and both transcriptional and translational initiation signals for rIIB. Mutants are being collected which alter each regulatory signal; comparative nucleic and sequencing of the wild type and mutant intercistronic regions is being used to define obligate sequences or structures needed for recognition of these signals.